Ignition sy tem for internal-combustion-micro-engines

ABSTRACT

An ignition system for internal-combustion micro-engines comprising an ignition magneto provided to energize a spark plug by means of an electric current fed through a contact breaker controlled by a cam and designed to become operative in conditions of maximum current, characterized by the fact that said magneto is so shaped and dimensioned as to be comprised within the engine clearance gauge, the inductor of said magneto being mounted into a housing defined between the blades of the engine fan which is fixed on the driving shaft, said inductor having its pole shoes set at a right angle to the rotation axis of the driving shaft, while the armature comprises a three leg core, where said legs are parallel to the said rotation axis and are simmetric with respect of a plane passing through said rotation axis, said armature core being constituted of a laminated iron structure, wherein the central leg which supports the primary and secondary winding, has a thickness smaller than that of the side legs which are identic, while the outer surfaces of said three legs are coplanar, the inductor being constituted of a two leg core, wherein the transverse centre plane passes through the axis or the fan rotor supporting said inductor, while the thickness of the inductor core legs is greater than that of the core legs of the armature so as to obtain towards the rotation axis of the ignition system a zone of electromagnetic leakage in order to produce a flattening of the peaks of the current curve.

United States Patent [191 Bonvicini [451 Sept. 17, 1974 IGNITION SYTEMFOR INTERNAL-COMBUSTION-MICRO- ENGINES [75] Inventor:

[73] Assignee: Fox Motori di CECI Napoleone &

C.s.a.s., Poviglio, Italy May 1, 1973 Giacomo Bonvicini, Poviglio, Italy[22] Filed:

I [21] Appl. No.: 356,088

[52] US. Cl. 310/70 A, 310/168 [51] Int. Cl. H02k 17/42 [58] Field ofSearch 310/70 R, 70 A, 153, 168, 310/268; 315/206, 209 R, 218

[56] References .Cited Primary ExaminerJ. D. Miller AssistantExaminerI-Iarry E. Moose, Jr. Attorney, Agent, or FirmWigman & Cohen[57] ABSTRACT An ignition system for internal-combustion microenginescomprising an ignition magneto provided to energize a spark plug bymeans of an electric current fed through a contact breaker controlled bya cam and designed to become operative in conditions of maximum current,characterized by the fact that said magneto is so shaped and dimensionedas to be comprised within the engine clearance gauge, the inductor ofsaid magneto being mounted into a housing defined between the blades ofthe engine fan which is fixed on the driving shaft, said inductor havingits pole shoes set at a right angle to the rotation axis of the drivingshaft, while the armature comprises a three leg core, where said legsare parallel to the said rotation axis and are simmetric with respect ofa plane passing through said rotation axis, said armature core beingconstituted of a laminated iron structure, wherein the central leg whichsupports the primary and secondary winding, has a thickness smaller thanthat of the side legs which are identic, while the outer surfaces ofsaid three legs are coplanar, the inductor being constituted of a twoleg core, wherein the transverse centre plane passes through the axis orthe fan rotor supporting said inductor, while the thickness of theinductor core legs is greater than that of the core legs of the armatureso as to obtain towards the rotation axis of the ignition system a zoneof electromagnetic leakage in order to produce a flattening of the peaksof the current curvev 4 Claims, 3 Drawing Figures PATENTEU SEPI 7 914SHEEI '1 UF 2 BAIENIEnsEmmn 3.886.800

QHEEI 2 OF 2 FIG. 2.

IGNITION SYTEM FOR INTERNAL-COMBUSTION-MlCRO-ENGINE the engine memberswhich are designed to perform 1 other functions.

Another object of the invention is to provide means adapted tocompensate for the disadvantages due to the reduction of the diameter ofthe rotating unit, either with respect of the mutual correlation betweenthe indu'ctor and the armature pertinent to said ignition system, or ofthe contact breaker operation.

It is known that the power which is necessary for the ignition of theair-full mixture is substantially independent of the engine pistondisplacement, since the produced spark substantially only serves toprime or start the combustion which then continues spontaneously.Commonly the sizes of the ignition unit remain unvaried, even if theengine dimensions decrease and as a re sult thereof the ignition unit ofthe micro-engines tends tooccupy more space than that of the main unit,i.e., that of the same engine. This unbalance between said dimensions islightly attenuated on account of the fact that in the explosionenginesof small or very small dimension, the compression torque is modest sothat also when manual strat devices are used, as for instance, astarting string, the driving shaft attains instantaneous considerablespeeds, that enabling within predetermined certain limits to constructmagnetos smaller that the normal ones, owing to the fact that theinduced voltages increase with the speed at which varies the magneticflux interlinked with the winding. However the dimensions of theignition unit remain, always conbeyond the clearance gauge of theengine. A three leg core 4, 4a has been provided so as to obtain acomplete reversal of the magnetic flux. Since parasitic currents in saidcore are produced, which are due to the high speed changes of theinterlinked currents, this core is realized by magnetic iron sheetshaving low losses. Therefore it will be necessary to provide a flatlaminated iron structure, where the pole pieces 6, 7 of the legs 4, 4aof the core are aligned on a plane substantially perpendicular to thecentre plane of the armature passing through the axis of the shaft 3,while the pole pieces of the two leg core 8 of the inductor whichaccording to the present invention is housed within recesses defined bythree adjacent rotor blades 2- which travel along a circular path(FIG; 1) which is of a small radius on account of the very small sizesof the engine which negatively affects the correct mutual facing of thepole shoes 6, 7 of the armature and those 5 of the inductor. In order toovercome said inconvenience which becomes more important as the rotordiameter of the rotor 1 decreases, according to this invention provisionhas been made to position a core 4, 4a of the siderable and negativelyaffect the possibility of constructing light microengines which occupylittle space, as are required for particular intended purposes, as, forinstance, for the production of portable mechanized tools.

For such a purpose this invention serves to eliminate the supportingmembers for the ignition unit, which is also so shaped and dimensionedas to be comprised within the clearance gauge of the engine.

Other features and advantages will be better under stood from thefollowing description of an embodiment of the invention which has to betaken in consideration "together with the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic view of the stationary and movable operatingmagnetic and electric devices of the ignition system, the engine fanrotor being partially broken away;

FIG. 2 is a diagrammatic section taken on the transverse centre plane ofthe armature passing through the axis of the driving shaft and saidfigure only showing 1 the devices of the induction system and of the fanrotor "which is used for supporting the rotating component ofsaidsystem; and

'. FIG. 3 is the diagrammatic section taken along the line A-A ofFIG.'2.

At 1 is marked the fan rotor provided with-a plurality of radial blades2 and which is mounted on the driving shaft 3. The'ignition systemcomprises an armature 1 having a core formed of three legs 4, 4a, whichextend parallelely to the axis of the driving shaft 3 and which are sopositioned and dimensioned as to do not project ing pole pieces 5.Therefore the side legs 4a have a thickness greater than that of thecentral leg 4 in order to compensate for the greater distance of thelegs 4a from the axis of the shaft 3 as compared with that of the arm 4and which is due to the provided aligned arrangement of all the outersurfaces of the legs 4, 4a. Also the pole shoes of the inductor 8 areformed by a number of iron sheets greater than that of the iron sheetsforming the central leg 4 of the armature, while their thicknessincreases toward the rotation axis. At 9 and 10 are marked the primaryand secondary windings of the armature and at 11 the condenser insertedin the ignition circuit. The rotor body 1 forms also a chamber 12 openedtowards the driving shaft 3 and in which is mounted the conventionalcontact breaker 13 and which is controlled by a cam 14, which, as theshaft 3 rotates, causes the closing and opening at predetermined timeintervals of the contacts of the breaker 13. The other devices of theignition system have not been illustrated since they are of conventionaltype. It is evident that is will be always necessary to perform anadjustment of the ignition system in order to obtain a correct angularpositioning between the stationary armature and the breaker 13 which istermed magnetic angle or inner phasing. This adjustment is madecritical-by the fact that, as well known, the electric degrees which areconcerned with the said mutual position are smaller than the mechanicdegrees, since the pole pitch of the development of the circular path ofthe inductor is a small fraction of the circular path length of the saidpole shoes, which is smaller as the engine size is reduced. Thecriticity of this adjustment is limited ,according to the presentinvention by realizing a curve of the induced current having flattenedpeaks and that is attained by arranging the parts in such a manner thatthe stationary pole shoes 6, 7 of the armature and the movable poleshoes 5 of the inductor 8 cross each other according to an inclineddisposition, thus producing also a considerable flux leakage due to theadvancing of the pole pieces 5 towards the axis of the shaft 3.

On account of the fact that the braker 13 must open in conditions ofmaximum current it will be apparent that such a flattening of the peaksallows to have at disposal a wider field amplitude of the break point.

I claim:

1. In an ignition system for intemal-combustion micro-engines comprisingan ignition magneto provided to energize a spark plug by means of anelectric current fed through a contact breaker controlled by a cam anddesigned to become operative in conditions of maximum current, whereinsaid engine includes a rotatable cooling fan spaced from said engine andmounted on a drive shaft, the improvement comprising a magneto shapedand dimensioned to be comprised within the engine clearance gauge, saidmagneto including an inductor mounted between the blades of the enginefan, said inductor including pole shoes set at a right angle to therotational axis of the driving shaft, an armature spaced from saidinductor comprising a three leg core, where said legs are parallel tothe said rotational axis, the central leg supports the primary andsecondary winding of said armature, and has a thickness smaller thanthat of the side legs, the inductor being formed of a two leg core, thethickness of the inductor core legs being greater than that of the corelegs of the armature, whereby a zone of electromagnetic leakage isobtained to yield a flattening of the peaks of the current curve.

said inductor pole piece confronting faces.

3. The magneto ignition system of claim 1 wherein said fan rotor furtherincludes ignition contact breaker means in electrical communication withsaid armature primary windings. v

4. The magneto ignition system of claim 1 wherein the inductor andarmature pole pieces have faces which are substantially rectangular inshape. =l

1. In an ignition system for internal-combustion micro-enginescomprising an ignition magneto provided to energize a spark plug bymeans of an electric current fed through a contact breaker controlled bya cam and designed to become operative in conditions of maximum current,wherein said engine includes a rotatable cooling fan spaced from saidengine and mounted on a drive shaft, the improvement comprising amagneto shaped and dimensioned to be comprised within the engineclearance gauge, said magneto including an inductor mounted between theblades of the engine fan, said inductor including pole shoes set at aright angle to the rotational axis of the driving shaft, an armaturespaced from said inductor comprising a three leg core, where said legsare parallel to the said rotational axis, the central leg supports theprimary and secondary winding of said armature, and has a thicknesssmaller than that of the side legs, the inductor being formed of a twoleg core, the thickness of the inductor core legs being greater thanthat of the core legs of the armature, whereby a zone of electromagneticleakage is obtained to yield a flattening of the peaks of the currentcurve.
 2. The magneto ignition system of claim 1 wherein said inductorpole pieces are positioned on a chord of said fan rotor beingsubstantially equidistant from said fan rotor axis, said armature polepieces having faces which confront said inductor pole piece faces suchthat upon rotation of said fan only a portion of the surfaces of saidarmature side leg pole pieces are traversed by said inductor pole piececonfronting faces.
 3. The magneto ignition system of claim 1 whereinsaid fan rotor further includes ignition contact breaker means inelectrical communication with said armature primary windings.
 4. Themagneto ignition system of claim 1 wherein the inductor and armaturepole pieces have faces which are substantially rectangular in shape.